In manufacturing processes of electronic components such as LSIs, fine patterning techniques utilizing photolithography have conventionally been adopted. Namely, a resist solution is firstly coated onto the surface of a substrate or the like to form a resist film; and the resist film is subjected to pattern-wise exposure to light, and then to treatments such as development by an alkaline developer to form a resist pattern. Subsequently, the bare surface of the substrate or the like is dry-etched by utilizing this resist pattern as an anti-etching mask to form minute lines and openings, and the remaining resist is finally removed by means of ashing.
Therefore, the resist herein used is generally required to have high dry-etching resistance. From this point of view, resists containing aromatic compounds have widely been used. Specifically, there have been developed a large number of resists containing, as base resins, novolak resins that are alkali-soluble.
On the other hand, in line with the trend toward high-density, high-integration LSIs and the like, the above-described fine patterning techniques have been improved in recent years so that patterning can be attained at the level of sub-half micron order; and this tendency toward fine patterning is expected to be more remarkable. Indeed, the wavelengths of light sources for use in photolithography are being made shorter; and it is now attempted to form fine resist patterns by using ArF excimer laser light (wavelength 193 nm), or a 5-fold higher harmonic wave of a YAG laser (wavelength 218 nm).
However, the resists containing, as base resins, resins containing aromatic compounds, which have commonly been used heretofore, have such a peculiarity that benzene nucleus contained in the compounds show high light absorption against the above-described short-wavelength light. Therefore, when it is tried to form a resist pattern, it is difficult to allow light to fully reach the substrate side of a resist film when the film is exposed to light. It has thus been difficult to form, with high sensitivity and high accuracy, patterns excellent in shape.
Under such circumstances, there is a strong demand for the development of highly transparent resist resins suitable also for photolithography which uses ArF excimer laser light, or a 5-fold higher harmonic wave of a YAG laser.
From this viewpoint, those resists containing alicyclic compounds in place of aromatic compounds are now attracting attention. Japanese Patent Laid-Open Patent Publication No. 39665/1992, for instance, describes the following example: alkali-solubility is imparted to a resist which is excellent in both dry-etching resistance and transparency against short-wavelength light and which comprises a compound containing adamantane that is a bridged-bond-containing alicyclic compound, by copolymerizing the resist and another acrylic compound; and a resist pattern is formed by alkali development, by the use of this alkali-solubility-imparted resist.
As shown in Japanese Patent Laid-Open Publication No. 199467/1995, there is known a resist material containing, as tricyclodecanyl structure, an alicyclic compound having 5-membered rings, which is one of bridged-bond-containing alicyclic compounds.
However, in the case where a resist pattern is formed by means of alkali development by the use of a resist containing such an alicyclic compound, various problems will be brought about. This is because the alicyclic structure such as adamantane skeleton has extremely high hydrophobicity, so that the difference in alkali-solubility between this alicyclic structure and a group which imparts alkali solubility to the resist is great.
For example, the predetermined area of the resist film cannot be uniformly dissolved and removed by development, so that the lowering of resolution is brought about. Moreover, the lowering of resolution is also caused due to the swelling of the resist pattern that occurs after development, and the resist film is cracked or undergoes surface roughening because even the area of the resist film that is supposed to remain after development is partly dissolved. Further, the separation of the resist pattern is often caused due to the penetration of an alkaline solution into the resist film-substrate interface. Furthermore, phase separation between the part having the alicyclic structure and the group which imparts alkali solubility, such as carboxylic acid moiety, tends to proceed in the polymer, so that it is difficult to obtain a homogeneous resist solution. In addition, such a resist solution shows poor coating performance.
In order to reduce the hydrophobicity of these alicyclic compounds, the introduction of a polar group such as COOH or OH group into the alicyclic compounds has been proposed (Japanese Patent Laid-Open Publications No. 83076/1998, No. 252324/1995 and No. 221519/1997). It has been confirmed that the solubility is considerably improved in all of these compounds.
However, the structure of these alicyclic compounds is such that COOH or OH group is combined with secondary or primary carbon atom of the aliphatic ring, so that this COOH or OH group tends to secondarily react with other substituents in the resists. Moreover, these compounds have low glass transition temperatures, so that they tend to bring about the lowering of resolution, and the swelling of the pattern after development.
An object of the present invention is therefore to provide, by overcoming the aforementioned problems, a resist resin which can be a component of a resist composition having high transparency against short-wavelength light and high dry-etching resistance, capable of forming a resist pattern excellent in adhesion and resolution by means of alkali development.
Another object of the present invention is to provide the above-described resist composition.
A further object of the present invention is to provide a pattern forming process using the resist composition.